Heating devices to prevent bacteria proliferation in the lowermost region of a water holding tank of an electric water heater

ABSTRACT

An electric water heater is described and wherein the bottom portion of the water holding tank is provided with various forms of electric heating elements to heat the water in the lowermost region of the tank adjacent the dome-shaped bottom wall to a temperature sufficient to prevent the proliferation of bacteria growth such as the Legionella bacteria in such lowermost region. The insulating foam support base of the water heater also provides a thermal barrier to the heating elements while biasing the heating element on the dome-shaped bottom wall in a region to insure excellent heat transfer to the cavitated zone surrounding the dome-shaped bottom wall where sedimentary deposits occur to create a culture medium for bacteria growth.

This is a divisional application of U.S. patent application Ser. No.15/731,956 filed on Sep. 1, 2017 and entitled Heating Devices to PreventBacteria Proliferation in the Lowermost Region of a Water Holding Tankof an Electric Water Heater.

FIELD OF THE INVENTION

The present invention relates to electric water heaters and particularlyto the prevention of bacteria proliferation in the lowermost region ofthe water holding tank of the water heater where water temperatures areat their lowest and wherein a cavitated area is formed about thedome-shaped bottom wall that creates a zone for the accumulation ofsedimentary deposits which can develop into a culture medium forbacteria growth.

BACKGROUND OF THE INVENTION

Although some species of Legionella bacteria can be found in the soil,most species live in water that is stagnant and wherein such bacteriasurvive under a wide range of temperatures. According to the Centers forDisease Control and Prevention, USA, between 8,000 and 18,000 people arehospitalized with Legionnaires disease each year. It is of great publicconcern as its fatality rate during an outbreak ranges from 5% to 30% inthose who contract the disease. Actively managing the risk of Legionellain water systems is more cost effective than responding to an outbreak.Outbreaks of Legionella pneumophila can stem from showers and potablewater systems. As water from such sources aerosolized, individuals caninhale the Legionella containing droplets and the organism is aspiratedinto the lungs.

The formation and multiplication of such Legionella bacteria is not onlypromoted by the temperature in the customary hot water systems, but alsoby the fact that dead spaces are present in such water distributionsystems in which deposits and sediment formation can arise, andtypically in the bottom zone of water heater tanks. Deposits therein canrepresent a culture medium for bacteria proliferation.

Most electric water heaters for domestic use have their water tankconstructed with a dome shaped bottom wall. Such dome-shaped bottomwalls form a surrounding cavitated zone about the dome-shaped wall wheresediments deposit can gather and where water is less agitated. Thiscavitated zone is spaced from the bottom heating element and thus watertherein is less hot which can create an ideal location for bacterialgrowth. Should the bottom element fail, then the water temperature atthe bottom of the tank will drop. It as also been determined by researchthat the Legionella bacteria does not survive at temperatures above 140degrees F. When hot water is not drawn from a water heater, the waterinside the tank becomes stagnant and the water temperature stratifieswith the cooler temperature being at the bottom region of the tank.Water within the cavitated zone below the bottom element of the tank canfall to about 85 to 105 degrees F. which is favorable to bacteriagrowth. It is said to be difficult to increase the temperature at thebottom of the tank when there is not water consumption. The solution tothe problem is to raise the temperature in the bottom end of the tank.However, lowering the bottom element to place it close to the bottomwall of the tank has not proven to be a viable solution.

Reference is made to U.S. Pat. Nos. 4,940,024; 5,168,546 and 5,808,277which disclose various methods and apparatus to prevent bacteriaproliferation in electric water heaters. One method teaches adding aheating element in the form of a belt or patch on the outside of thetank against the bottom end of the outer sidewall of the tank to heatthe water at the bottom end of the tank to a temperature preferablyabove 55 degrees C. (130 degrees F.). Accordingly, this proposedsolution provides an extra heating element in the form of one or moreelectrical patch heaters located in an area which is usually filled withinsulating foam material and not practical to access should it fail andrequire replacement or repair. Providing a large access panel for accessto such elements is not practical as the expandable foam would cover theelements and if a large foam dam is used then there will be considerableheat loss in that region. It is not a practical solution and it is alsocostly and consumes more electricity. In U.S. Pat. No. 5,808,277 a thirdelement is added into the tank to periodically raise the watertemperature at the bottom of the tank beyond the pre-set consumptiontemperature, to a sanitizing temperature to destroy bacteria. This isalso a costly proposition. U.S. Pat. No. 4,940,024 discloses a method ofdirecting the cold water flow of all consumed drinking or domesticallyused water through the lower region of the tank wherein there is nostagnant water and wherein no deposits can be formed for bacteriagrowth. Accordingly, the lower region of the tank is continuouslyflushed with fresh water. This is a costly solution requiring a new tankdesign and cold water conduit network and therefore not a viablesolution.

SUMMARY OF THE INVENTION

It is a feature of the present invention to provide an electric waterheater with controllable heating devices secured in the lower region ofthe tank in the area of the dome-shaped bottom wall to maintain thetemperature of water in the immediate area of the dome-shaped bottomwall at a temperature range wherein harmful bacteria such as theLegionella bacteria will not survive.

Another feature of the present invention is to incorporate a resistiveheating element in the form of a heating film or a heating wire or ashaped rigid resistive heating element in a cavitated formation formedin a top surface of a dome portion of a rigid foam insulating supportbase to position the heating element in direct contact against thedome-shaped bottom wall of the tank to heat the bottom wall and thewater there against at a temperature sufficient to prevent harmfulbacteria growth in the lowermost region of the water holding tank.

Another feature of the present invention is to provide automatic controlof the heating elements mentioned in the previous paragraph toindependently heat the water in the lowermost region of the tank andwherein the automatic control may be a remote controller or a thermostatlocated in a cavity of the insulating support base and having atemperature sensor thereof biased against the tank bottom wall.

A still further feature of the present invention is to provide a conduitof thermally conductive material secured about a substantial lowermostportion of the side wall of the water holding tank of an electric waterheater and wherein a heating wire of predetermined power density isremovably retained in the conduit.

Another feature of the present invention is to provide an electricheating element in contact with the lower region of the water holdingtank against the dome-shaped bottom wall of the tank or the surroundingside wall of the tank in the region of the bottom wall and wherein theelectric heating element is in thermal contact with the tank andinsulated from the outside by thermally insulating foam material withthe heating element operated for a predetermined time periods sufficientto raise the temperature of water in the lowermost portion of the tankto a temperature wherein harmful bacteria cannot survive.

A still further feature of the present invention is to support aresistive heating element in the cavitated circumferential area definedbetween a lower end portion of the tank side wall and the dome-shapedbottom wall to heat water in the immediate area of the dome-shapedbottom wall to a temperature sufficient to sanitize the tank in itslowermost region to prevent bacteria growth in the cavitated area.

According to the above features, from a broad aspect, the presentinvention provides an electric water heater which is comprised of awater holding tank having a cylindrical side wall, a top wall and adome-shaped bottom wall. A cold water inlet is disposed for releasingwater under pressure in a lower portion of the tank. Two or moreresistive heating elements heat water in an upper and a lower region ofthe tank. A thermostat, having a temperature sensor and a control, isassociated with each of the two or more resistive heating elements tocontrol the operation of the resistive heating elements to heat waterwithin the tank regions to pre-set desired temperatures. An insulatingsupport base is fitted at a bottom end of the water holding tank andshaped and disposed for contact with an outer surface of the dome-shapedbottom wall. A controllable electric heating means is interposed betweenthe insulating support base and the outer surface of the dome-shapedbottom wall to heat water in the tank in the immediate area of thedome-shaped bottom wall to a temperature sufficient to sanitize the tanklower region.

According to another broad aspect of the present invention a spiralcavity is formed in an outer face of the surrounding lower portion ofthe insulating support base and shaped for housing a heating wireconstituting a controllable heating means. The spiral cavity positionsthe heating wire in flush contact with the dome-shaped bottom walladjacent an inner cavitated circumferential area of the dome-shapedbottom wall of the tank. A control means is provided for controlling thepower supply to the heating wire.

According to another broad aspect of the invention a circular cavity isformed about the outer face of the surrounding lower portion of the domeportion of the insulating support base and shaped for housing a rigidcircular shaped resistive heating element in close fit therein. Thecircular resistive heating element has a space defined between opposedadjacent connector ends thereof for securing conductors to a powersupply to energize the circular resistive heating element.

According to a still further broad aspect of the invention there isprovided an electric water heater comprised of a water holding tankhaving a cylindrical side wall, a top wall and a dome-shaped bottomwall. A cold water inlet is disposed for releasing water under pressurein a lower portion of the tank. Two or more resistive heating elementsare provided to heat water in an upper and lower region of the tank. Athermostat, having a temperature sensor and a control, is associatedwith each of the two or more resistive heating elements to control theoperation of the resistive heating elements to heat water within thetank regions to pre-set desired temperatures. A conduit of thermallyconductive material is secured about at least a substantialcircumferential portion of an outer surface of the cylindrical side walladjacent the dome-shaped bottom wall. A resistive heating wire isdisposed in the conduit and has connection leads extending out of a freeopen end of the conduit to an access area to provide connection to powerterminals and control means. The control means controls the supply ofpower to the resistive heating wire.

According to another broad aspect of the present invention there isprovided an electric water heater having a bacteria preventive featureto prevent bacteria growth in the cavitated area at the bottom of thetank.

DESCRIPTIONOF THE DRAWINGS

A preferred embodiment of the present invention will now be describedwith reference to the examples thereof as illustrated by theaccompanying drawings in which:

FIG. 1 is a simplified schematic illustration, partly fragmented andexploded, showing a water holding tank of an electric water heater ofthe prior art supported on an insulating support base;

FIG. 2 is a side view of a dome shaped support base modified inaccordance with the present invention to support and position afilm-type heating element therein and a thermostat for the control ofthe heating element;

FIG. 3 is a top view of the dome shaped support base of FIG. 2 butmodified wherein the control is an automatic control device locatedexternally of the support base;

FIG. 4 is an enlarged view illustrating a cavity passage formed in theinsulating support base for the passage of wires under the surroundingbottom edge of the water holding tank;

FIG. 5 is a top view of the insulating support base wherein a spiralchannel is formed in the top surface of the support base for housing aheating wire in spiral form therein;

FIG. 6 is a top view, similar to FIG. 5, but wherein the insulatingsupport base has been modified to support a thermostat and associatedwiring and connections;

FIG. 7 is a fragmented side view of the insulating support base of FIG.6 illustrating the cavities and channels formed therein for the passageof wiring to connect to an external controller;

FIG. 8 is a top view of a circular resistive heating element shaped forattachment in an insulating support base of an electric water heater;

FIG. 9 is a fragmented sectional view of a bottom outer region of awater holding tank resting on an insulating support base in which thecircular resistive heating element of FIG. 8 is secured in closesnap-fit in a circular cavity formed in the outer surface of the domebottom portion of the support base to position the resistive heatingelement in contact with the dome-shaped bottom wall of the tank andwherein a heat conductive paste is positioned in the voids about theresistive heating element;

FIG. 10 is an enlarged view of the region of the resistive heatingelement shown in FIG. 9 located in its retention cavity;

FIG. 11 is a fragmented sectional view of an example of a heatingelement secured about the outer surface of the water holding tank sidewall in the area adjacent the dome-shaped bottom wall of the tank andwherein a heating wire is removably positioned within a thermallyconductive conduit secured to the tank side wall;

FIG. 12 is a fragmented side view illustrating an embodiment for thecontrol of the heating element of FIG. 11;

FIG. 13 is a simplified side view showing the shape of an end section ofthe conduit to provide access thereto for the insertion and removal ofthe heating wire;

FIG. 14 is a fragmented sectional view illustrating a still furtherembodiment of the present invention wherein a resistive heating elementis supported inside the tank and in the cavitated circumferential areadefined between a lower end portion of the side wall of the tank and thedome-shaped bottom wall;

FIG. 15 is a side view illustrating the shape and construction of theresistive heating element of FIG. 14, and

FIG. 16 is a top view of FIG. 15.

DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION

Referring now to the drawings and more particularly to FIG. 1, there isshown a schematic illustration of a water holding tank 10 of an electricwater heater and sized to contain a predetermined volume of water to beheated. The water holding tank 10 is constructed of steel material anddefines a circumferential side wall 11, a top wall 12 and a dome-shapedbottom wall 13. Two or more resistive heating elements, herein thebottom resistive heating element 14 being shown, extend with the waterholding tank to heat water in the upper region 15 and bottom region 16of the tank. Each of the resistive heating elements have a thermostat 17associated therewith and provided with a temperature sensor and control,not shown but obvious to a person skilled in the art, for the operationof the resistive heating elements 14 to heat water within theirrespective regions of the tank to preset temperatures set within thecontrol of the thermostat, usually at 140 degrees F. When water is drawnfrom the top end of the tank through a hot water supply conduit 18, coldwater from the domestic water supply is introduced in the bottom region16 of the tank via a dip tube 19. The water holding tank 10 is insulatedby expandable foam material 20 injected between the tank 10 and an outershell 21 of the water heater. As illustrated, the water holding tank 10is supported on an insulating rigid foam support base 22 which is shapedfor contact with the dome-shaped bottom wall 13 of the tank to thermallyinsulate and provide support to the dome-shaped bottom wall of the tank.The support base 22 has a dome support portion 23 and a circumferentialouter support flange portion 24 on which the lower edge of the tank sidewall is also supported. The flange portion 24 extends for close fit withthe inner surface of the outer shell 21 onto which the foam 20 expandsto. Thus, is a brief description of a prior art water holding tank 10and insulation of the tank of an electric water heater.

With reference now to FIGS. 2 to 4 there is shown an example of aheating means associated with insulating support base 22 for heating thedome-shaped bottom wall 13 of the water holding tank 10. As hereinillustrated the heating means is in the form of a resistive film-typeelectric heating element 25 which is fitted and glued within a shallow,belt-shaped, surrounding cavity 26 formed in an outer face 27 of asurrounding lower portion of the dome portion 23 of the insulatingsupport base. The cavity 26 has a depth wherein when the tank 10 ispositioned over the insulating support base 22, the film-type resistiveheating element 25 is in direct contact with the outer surface 29 of thedome-shaped bottom wall 13 to provide direct heat transfer to the bottomwall 13. As herein shown, the cavity 26 is disposed in a lower area ofthe dome portion 23 of the support base whereby to heat the dome-shapedbottom wall 13 of the tank in a cavitated circumferential area 30defined between a lower end portion 31 of the tank 10 circumferentialside wall 11 and the dome-shaped bottom wall 13.

As shown in FIGS. 2 and 3, the thin film-type heating element has one ormore resistive heating wires 32, herein one sinusoidal shaped wire, andconnection leads 33 secured to a connection terminal 34 to which powersupply leads 35 are connected to. The connection terminal 34 is alsolocated in an appropriate cavity formed in the support base. The cavity26 is formed with a flat bottom wall 36 shaped to extend parallel to thedome-shape bottom wall 13. As shown in FIG. 3, a reflective substrate 37may be glued on the flat bottom wall 36 of the cavity or may belaminated to the film-type heating element 25 whereby to reflect heat inthe direction of the dome-shaped bottom wall. Of course, the insulatingsupport base is molded from a suitable styrene foam material capable ofresisting to the heat generated by the heating element 25.

As shown in FIG. 2 a thermostat locating cavity 38 is formed in the domesection 28 of the support base 22 to position a control thermostat 39therein for close fit of its sensor 40 against the outer surface 29 ofthe dome-shaped bottom wall 13 to sense the temperature of the bottomwall 13 which is substantially the same as the water inside the tankagainst the bottom wall. A power supply cable 41 extends in a protectivechannel 42 and connects power to the thermostat 39 which controls thefilm-type heating element 25 to maintain the water temperature insidethe tank in the region of the bottom wall 13 at a set desiredtemperature sufficient to prevent harmful bacteria proliferation, forexample 140 degrees F. FIG. 3 shows another control for the resistiveheating film 25 wherein the cable leads 35 connect externally to aswitch 43 which is operated by a controller device 44 which receivestemperature value signals from a sensor 45 secured to the tank outersurface adjacent the cavitated area 30. The controller is programmed tomaintain the predetermined temperature in the tank lower portionadjacent the dome-shaped bottom wall. Other functions can be programmedwithin the memory of the controller to interface with a remote locationsuch as the grid provider. A timer circuit may be associated with thecontroller if programmed to operate the heating element duringpredetermined time periods and predetermined programmed occurrences ofthe electric water heater

Referring now to FIGS. 5 to 7, there is illustrated another embodimentof the invention wherein the heating element is in the form of a spiralheating wire 50 which is held in tight fit or glued into a spiralchannel 51 formed in the outer surface 52 of the dome portion 53 of theinsulating support base 54, which is similar to the insulating supportbase 22 of FIG. 2. Also, a thermostat locating cavity 55 may be formedto house a thermostat 56 therein. However, if the water heater isequipped with an intelligent controller, by noticing a temperatureincrease from 140 degrees F. to 141, it will provide an indication thatthe sanitation cycle is done. Channels 56 are also formed to accommodatethe wiring and connectors as with the FIG. 2 embodiment. The operationof the spiral wire heating wire can also be controlled by a remotecontroller 57 operating the same as the controller 44 of FIG. 3.

With reference now to FIGS. 8 to 10, there is illustrated an anotherversion of the invention wherein the heating element is a resistiveheating element commonly found in water heaters but wherein the elementis formed as a circular resistive heating element 60 which is retainedin close snap-fit engagement in a circular cavity 61 formed about theouter face 62 of the surrounding lower portion 63 (see FIG. 1) of thedome portion 23 insulating support base 22. The circular resistiveheating element 60 has a space 63 defined between opposed conductor ends64 thereof for the leads 65 to secure to a connector 66 to which powercan be connected in a similar fashion as with the previous embodimentsdescribed above.

As better seen in FIG. 10, the circular cavity 61 has an arcuate bottomwall 67 and an upwardly curved upper side wall 68 shaped to provide easysnap-fit entry of the circular resistive heating element 60 therein fromabove the base. A heat conductive paste 69 of a type well known in theart and suitable for this application, is applied over the resistiveheating element and surrounding open top end areas 70 to fill the voidsand provide good heat transfer to the dome-shaped bottom wall of thetank.

Alternatively, or in combination therewith, a heat reflective substrateor film 71 may be glued within the circular cavity 61. The connectionsand operation of the circular resistive heating element is the same aswith the other resistive heating elements described above.

Referring now to FIGS. 11 to 13 there is illustrated a differentembodiment wherein a heating wire 80 is removably retained inside aconduit 81 formed by a U-shaped non-conductive material, such as plasticor other suitable material, and which is secured about at least asubstantial circumferential portion of the outer surface 82 of thecylindrical side wall 83 of the water holding tank of an electric waterheater. The conduit 81 extends in a lower region of the tank adjacentthe dome-shaped bottom wall 85 adjacent the circumferential cavitatedzone 84 defined between the bottom end section 86 of the tank side wall83 and the dome-shaped bottom wall where sediments 88 collect to createa culture zone for bacteria growth. The U-shaped conduit 81 may be madeof flexible material capable of being curved over the curved side wall83 or be pre-formed as a curved conduit.

As shown in FIG. 11 the conduit 81 may be immovably retained against theside wall 83 by a suitable adhesive tape 90, or tape portions. The tapeand the conduit is also held immovable by the expandable insulating foam93 injected in the space between the tank outer wall and the outer shell94. A reflective tape (not shown) can also be held against the conduit80 to reflect heat towards the tank side wall 83.

As shown in FIGS. 12 and 13, the conduit 81 has an upwardly curved endsection 87 with a free open top end 95 which terminates in the accessopening 96 of the bottom resistive heating element 14, see FIG. 1. Theheating wire 80 is inserted into the conduit 81 through this open topend 95 and is connected to power terminals of the terminal block 97 ofthe lower thermostat 17 through which power is rendered accessible bysuitable controls such as the controller 98 illustrated in FIG. 12through which power is provided when necessary to do so as determined bymonitored signals received from water temperature sensor 99. Therefore,access is provided to the heating wire 80 for replacement if necessaryand connection to a supply without having to form another access openingbetween the tank and the outer shell and providing an additional accesspanel.

Referring now to FIGS. 14 to 16 there is shown a still furtherembodiment of the present invention wherein a bottom resistive heatingelement 100 is shaped to extend at least partly within the cavitatedcircumferential area 30 defined between the tank side wall 11 and thedome-shaped bottom wall 13. As better illustrated by FIGS. 15 and 16,the bottom resistive heating element 100 has a circular shape 101 withspaced opposed free end sections 102 each shaped as an upwardlyextending goose-neck 103 to which is secured a connecting flange 104spaced form the free ends 105. The free ends 105 extend through asecurement hole in the tank side wall with a water-proof gasket 106disposed against the flange 104 and an inner face 108 of the side wall11. An outer connecting flange assembly 107 holds the connecting flangein pressure engagement with the inner surface 108 of the side wall toposition the bottom resistive heating element 100 is a substantiallyhorizontal plane in the cavitated circumferential area 30 and closelyspaced to the inner face 108 of the side wall. The bottom element is alow watt density heating element and preferably secured to the tank wallby a dielectric connector assembly 107 formed of material made of copperor stainless, incoloy, inconel, or any other suitable material toprevent corrosion. The bottom resistive heating element 100 is installedbefore the dome-shaped bottom wall and must be positioned as low aspossible but high enough to prevent interference during the assemblyprocess of the dome-shaped bottom wall 13 with the tank side wall 11.

In all embodiments described herein the heating means is arranged suchas to heat the water within the lowermost portion of the tank includingthe cavitated circumferential area to a temperature of 140 degrees F.and for a sufficient time to kill the Legionella bacteria. These heatingmeans may also be operated during non-peak hours when electricity isplentiful and costs are lower.

It is within the ambit of the present invention to cover anymodifications of the preferred embodiments described herein providedsuch modifications fall within the scope of the appended claims.

1. An electric water heater comprising a water holding tank having a cylindrical side wall, a top wall and a dome-shaped bottom wall; a cold water inlet disposed for releasing water under pressure in a lower portion of said tank, two or ere more resistive heating elements to heat water in an upper and lower region of said tank, a thermostat having a temperature sensor and a control associated with each said two or more resistive heating elements to control the operation of said resistive heating elements to heat water within said tank regions to pre-set desired temperatures, an insulating support base at a bottom end of said water holding tank and shaped and disposed for contact with an outer surface of said dome-shaped bottom wall; and controllable electric heating means interposed between said insulating support base and said outer surface of said dome-shaped bottom wall to heat water in said tank in the immediate area of said dome-shaped bottom wall to a temperature sufficient to sanitize said tank lower region to prevent the proliferation of harmful bacteria, said insulating support base has a solid dome portion in contact with said outer surface of said dome-shaped bottom wall with said controllable electric heating means being interposed between a lower area of said dome portion and a cavitated circumferential area defined between a lower end portion of said tank circumferential side wall and said dome shaped bottom wall, a circular cavity is formed in an outer surface of said surrounding lower portion of said insulating support base and shaped for housing said controllable heating means therein wherein said controllable heating means is positioned adjacent said cavitated circumferential area, and control means for controlling the operation of said controllable heating means, said controllable heating means being a resistive heating element positioned in close fit in said circular cavity, said resistive heating element constituting said controllable heating means, said circular resistive heating element having opposed conductor ends for securement to a power supply to energize said resistive heating element.
 2. The electric water heater as claimed in claim 1 wherein a reflective substrate is positioned in said circular cavity for reflecting heat from said resistive heating element against said surrounding lower portion of said dome-shaped bottom wall.
 3. The electric water heater as claimed in claim 1 wherein a thermally conductive paste is disposed over said resistive heating element and surrounding open top end areas of said circular cavity to fill voids to provide heat transfer to said dome-shaped bottom wall.
 4. The electric water heater as claimed in claim 1 wherein said resistive heating element is a substantially circular resistive heating element, said outer face of said surrounding lower portion of said dome-shaped insulating support base is a downwards and outwardly curved-shaped surface, said circular cavity having an arcuate bottom wall and an upwardly curved upper side wall shaped to provide snap-fit entry of said circular resistive heating element into said circular cavity.
 5. The electric water heater as claimed in claim 1 wherein said circular cavity is a spiral cavity formed in said outer surface of said surrounding lower portion of said insulating support base and shaped for housing a heating wire constituting said resistive heating element formed by a spiral heating wire, said spiral cavity positioning said spiral heating wire in contact with said dome-shaped bottom wall adjacent said cavitated circumferential area, and control means for controlling the power supply to said heating wire.
 6. The electric water heater as claimed in claim 5 wherein a thermally conductive paste is disposed over said heating wire from an open top end of said spiral cavity to fill voids about said heating wire and conduct heat from said heating wire to said dome-shaped bottom wall.
 7. The electric water heater as claimed in claim 1 wherein said control means is one of a thermostat secured to an outer surface of said water holding tank adjacent said dome-shaped bottom wall, and a controller associated with temperature sensing means and/or a timer and programmed to manage the operation of said controllable heating means.
 8. The electric water heater as claimed in claim 1 wherein said insulating support base is molded from a thermally insulating material and defines a circumferential outer support flange portion on which a lower edge of said tank side wall is supported. 